Solid state lighting (SSL) is rapidly becoming the norm in many lighting applications. This is because SSL elements such as light emitting diodes (LEDs) exhibit superior lifetime and energy consumption compared to traditional alternatives such as incandescent and fluorescent lighting devices, e.g. light bulbs.
However, there are still difficulties to overcome in order to improve customer satisfaction and increase market penetration. For instance, SSL element-based lighting devices are often perceived to create light that is less aesthetically pleasing compared to traditional alternatives. For instance, the filament of an incandescent light bulb produces more or less omnidirectional light whereas SSL elements tend to produce light under a range of angles of 180° or less due to the fact that the SSL elements can be considered point sources mounted on a carrier surface, wherein the light is generated away from the surface.
This means that for a SSL element-based lighting device such as a light bulb, additional measures must be taken to emulate the omnidirectional luminous distribution from its traditional counterparts. This may for instance be achieved using additional optical elements, e.g. reflectors. However, the integration of such additional optical elements tends to compromise the aesthetic appearance of the lighting device.
In addition, in order to achieve a luminous output that is equivalent in intensity to a traditional counterpart, a SSL element-based lighting device typically comprises a plurality of SSL elements. Such elements generate a significant amount of heat, which needs to be effectively dissipated in order to maintain the operating temperature of the SSL element-based lighting device within a desired range, e.g. to avoid the temperature-dependent colour variation in the luminous output of the SSL elements. To this end, the SSL element-based lighting device typically comprises a metal heat sink thermally coupled to the SSL elements. An example of a LED bulb including such a heat sink is shown in CN 201 954 317 U. However, such a heat sink is unsightly as well as costly and clearly distinguishes the appearance of the SSL element-based lighting device from its traditional counterparts. This hampers the market penetration of SSL element-based lighting devices.